The U.S. Environmental Protection Agency (EPA) recently proposed to renew the city of San Diego’s discharge permit for the E.W. Blom Point Loma Metropolitan Wastewater Treatment Plant and Ocean Outfall. Under the proposal, the city would continue to operate its municipal wastewater treatment plant and ocean outfall under a variance from federal secondary sewage treatment standards.

“Today we have made a tentative determination that the city of San Diego may continue its discharge from the Point Loma treatment plant under a Clean Water Act variance from secondary treatment,” said Wayne Nastri, the EPA’s administrator for the Pacific Southwest region. “The city’s application demonstrates that plant operations, including the recent upgrade to disinfect treated wastewater, result in a discharge that protects recreational users of San Diego’s ocean waters and ensures a healthy marine ecosystem.”

San Diego’s Point Loma plant is currently operating under a variance from the Clean Water Act’s secondary sewage treatment standards. If the state of California concurs, and the EPA proposal becomes final, a renewed permit incorporating a variance will be issued.

The EPA’s tentative decision, along with the draft permit for renewal, will be available for public comment through January 28. A public hearing, conducted by both the EPA and San Diego Regional Water Quality Control Board, on the EPA’s tentative decision and the draft permit, will be held on Jan. 21 at 9 a.m. at the regional board’s office. At the completion of the public comment period, the EPA will consider all public comments and make a final decision on the city’s variance request.

As a general matter, primary treatment involves screening out large floating objects such as rags and sticks, removing grit, such as cinders, sand and small stones, and allowing wastewater to settle, followed by removal of collected solids. When secondary treatment is used, primary-treated wastewater flows into another process, where a large portion of the organic matter in the wastewater is removed by making use of the bacteria in the sewage. There are a variety of different biological treatment techniques that allow the bacteria to consume most of the wastewater’s organic matter.

The Point Loma plant operates as a chemically assisted primary wastewater treatment plant. At Point Loma, the primary treatment process is enhanced by the addition of chemicals that improve the solids settling process. Chlorine is added to the treated wastewater prior to its discharge via an outfall pipe terminating 4.5 miles off the Pacific Coast, at a depth of approximately 300 ft.

The Clean Water Act generally requires municipal sewage treatment plants to use both primary and secondary treatment. Amendments to the Act in 1977 and 1994 continue to allow the city to apply for a variance from federal secondary sewage treatment standards for the Point Loma plant, provided the plant meets water quality standards and other specific statutory criteria.

Under the terms of the proposed permit, San Diego will be able to continue its current level of sewage treatment, with the addition of chlorination. The proposed permit sets specific parameters for wastewater discharge and monitoring that ensure protection of offshore waters. The discharge permit, including the variance from secondary sewage treatment standards, is renewable every five years.